The present invention was developed for systems of the type shown in U.S. Pat. No. 3,941,936 issued Mar. 2, 1976 to K. Graham et al and in U.S. Pat. No. 3,997,738 issued Dec. 14, 1976 to V. Korsky et al. In the system shown by those patents, the main memory is a recirculating one in which various system functions are performed during one of a group of time slots allotted for that function. Switching from function to function occurs during a predetermined group of time slots in which the addresses of the stations involved in call processing are transferred from one time slot to a new time slot representing the function to be performed by the system.
In such systems, noise entering the system can produce binary data errors, or such errors can be produced through other means. Such errors can cause lost or dropped calls and other problems injurious to proper call handling.